The tire diameter of the vehicle wheel is needed to ascertain the vehicle speed and/or the distance that a vehicle has travelled. The respective information on the tire diameter is stored in at least one control device. This value can be utilized in conjunction with a value indicating the wheel revolutions and supplied by a wheel revolution sensor to calculate the value for the vehicle speed and/or the value for the distance the vehicle has travelled. This value for the vehicle speed or the distance travelled is used by vehicle systems such as automatic or semi-automatic parking assistants, in order to calculate the position of the vehicle at any point in time and to calculate the distance required for the parking manoeuver. Any error regarding the tire diameter therefore results in an error when determining the vehicle position or the distance travelled.
When changing from summer tires to winter tires or vice versa considerable differences may occur regarding the tire diameter. Therefore the tire diameter must be regularly calibrated. Normally the tire diameter or the tire circumference is measured and the measured value is directly programmed into the corresponding control device. The circumference of the tire calculated on this basis does, however, not normally indicate the actual tire circumference of the assembled vehicle wheel.
A method for calibrating the wheel diameter or the wheel circumference is described in the DE 10 2005 054 141 A1. Accordingly a reference distance is travelled and the wheel rotations required for this are set in relation to the distance travelled for calculating therefrom the wheel diameter or the wheel circumference. Similarly it is known from the DE 10 2005 052 476 A1 to determine the wheel circumference from the signals of a wheel revolution sensor and a reference distance. In here it is proposed to determine the reference distance from the positions ascertained by the GPS system of a navigation system.
Now, in order to determine the wheel circumference or the wheel diameter using these methods, a relatively high accuracy is preferable when determining the reference distance, which causes corresponding systems to always be complicated and thus cost-intensive.
Against this background it is at least one objective to provide a method for ascertaining the wheel circumference, which delivers high accuracy when ascertaining the reference distance for determining the wheel circumference or the wheel diameter. In addition, other objects, desirable features and characteristics will become apparent from the subsequent summary and detailed description, and the appended claims, taken in conjunction with the accompanying drawings and this background.
Accordingly there is provided a method for ascertaining a wheel circumference of at least one vehicle wheel attached to a vehicle with a reference distance travelled by the vehicle and with the measuring signals of a wheel revolution sensor associated with the vehicle wheel, comprising the following consecutively executed steps: positioning the vehicle in front of a stationary obstacle with a distance measuring device of the vehicle, moving the vehicle in direction of the obstacle, ascertaining the distance travelled as the reference distance with the distance measuring device, ascertaining the number of measuring pulses of the wheel sensor over the distance travelled, determining the wheel circumference from the ascertained distance and the ascertained number of measuring pulses of the wheel sensor.
A parking assistance system of a motor vehicle with a control device, distance sensors and wheel revolution sensors respectively associated with the vehicle wheels of the vehicle for performing a method according to an embodiment. A motor vehicle with a parking assistance system according to an embodiment. A computer program comprising instructions causing the program-controlled device to execute a method according to an embodiment. A computer-readable medium comprising a computer program according to an embodiment.
At least one of the embodiments is based on the knowledge that the reference distance required for calculating the wheel circumference can be ascertained with a great deal of accuracy. If this variable is utilized for calculating the wheel circumference, this will also lead to an accurate value for the calculated wheel circumference, as a result of which assistance systems of the vehicle utilizing this value of the wheel circumference can reliably operate with a high degree of quality. Advantageous embodiments and further developments are the subject of the sub-claims and of the description with reference to the figures.
With an advantageous design of the embodiments provision is made for a wheel revolution sensor to be associated with each vehicle wheel and for method step to be performed for each vehicle wheel. Preferably the measuring pulses determined for each vehicle wheel are then used in method step to ascertain the wheel circumference of the vehicle wheels. This offers the advantage of individually determining the circumference of each wheel and to evaluate these values as regards further tire parameters such as tire pressure.
It is particularly advantageous if in the further embodiment a mean wheel circumference is determined from the ascertained wheel circumferences of the vehicle wheels. This value can be used by vehicle systems such as a parking assistance system to improve the result and which according to an advantageous further development of the invention comprises a distance measuring device. Initially the parking assistance system is placed into a learning mode in order to perform the method according to an embodiment.
In one embodiment provision is made for a factor to be determined during determination of the wheel circumference which factor characterizes the relationship between the determined wheel circumference and the stored wheel circumference. Using this calculated factor a plurality of vehicle systems can very easily calculate the newly determined wheel circumference and utilize it for its further operation.
The above embodiments and further developments can be combined in any given meaningful way. Further possible arrangements, further developments and implementations of the invention also comprise not explicitly mentioned combinations of previously or subsequently mentioned features in relation to the embodiments. In particular the expert will add individual aspects as improvements or amendments to the respective basic design.